Add Optimism endpoint

Author: jlin27

mdx/api/index.mdx

@@ -16,6 +16,7 @@ We offer hosted versions for different Ethereum networks. Requests for more netw
 | Avalanche           | https://avalanche.api.0x.org/ |
 | Fantom              | https://fantom.api.0x.org/    |
 | Celo                | https://celo.api.0x.org/      |
+| Optimism            | https://optimism.api.0x.org/  |
 
 ## Versioning
 
@@ -80,7 +81,7 @@ The following table includes commonly used contract addresses. For a full list o
 | Avalanche           | https://avalanche.api.0x.org/ | 0xdef1c0ded9bec7f1a1670819833240f027b25eff | 0x0000000000000000000000000000000000000000 | 0x0000000000000000000000000000000000000000 |
 | Fantom              | https://fantom.api.0x.org/    | 0xdef189deaef76e379df891899eb5a00a94cbc250 | 0x0000000000000000000000000000000000000000 | 0x0000000000000000000000000000000000000000 |
 | Celo                | https://celo.api.0x.org/      | 0xdef1c0ded9bec7f1a1670819833240f027b25eff | 0x0000000000000000000000000000000000000000 | 0x0000000000000000000000000000000000000000 |
-
+| Optimism            | https://optimism.api.0x.org/  | 0xdef1abe32c034e558cdd535791643c58a13acc10 | 0x0000000000000000000000000000000000000000 | 0x0000000000000000000000000000000000000000 |
 
 ## Errors